Vector Network Analyzers (VNAs) enable vector responses of many types of electrical and optical devices to be accurately characterized. However, presently available VNAs are not well suited for vector characterization of mixers, modulators, and other types of frequency translation devices. Frequency translation devices (FTDs) provide output signals at frequencies that are different from the frequencies of input signals that are applied to the FTDs, resulting in inaccuracies in the characterization of FTDs, caused by impedance mismatches, response unflatness and lack of phase reference inherent in the VNAs. Because FTDs are critical to the performance of communication systems in which they are included, there is a need for a system that enables accurate characterization of the vector, or magnitude and phase, responses of FTDs.
A vector stimulus/response system constructed according to the preferred embodiment of the present invention enables the magnitude and phase responses of FTDs to be accurately characterized. The system includes a source, having a predetermined source match, reflection tracking and directivity, that generates a stimulus signal. A receiver having a predetermined load match is also included in the vector stimulus/response system. The receiver measures a first series of responses of a reference translator to the stimulus signal, when the reference translator is coupled between the source and receiver. The reference translator has predetermined transmission characteristics, input match and output match. The receiver measures a second series of responses of a FTD to the stimulus signal when the FTD is coupled between the source and the receiver. A processor generates a correction array from the first series of responses, the predetermined transmission characteristics, input match output match, source match, and the directivity, reflection tracking and load match. The processor then applies the generated correction array to modify the second series of responses to provide vector characteristics of the FTD.
In a first preferred embodiment of the present invention, a phase coherent reference and an amplitude reference for the receiver are provided by a parallel reference path having a reference FTD. In a second preferred embodiment of the present invention, a phase coherent reference and an amplitude reference for the receiver are provided by a series complimentary reference path having a reference FTD performing an up-conversion when the reference translator and the measurement FTD down-convert the stimulus signal, and performing a down-conversion when the reference translator and the measurement FTD up-convert the stimulus signal. The preferred embodiments of the present invention are alternatively implemented according to a method for vector characterization of frequency translation devices.